Reducing dusting in the manufacture of coated paper



Patented Mar. 2, 1937 PATENT OFFICE REDUCING DUSTING IN THE MANUFAC- TUBE OF COATED PAPER Louis C. Fleck, Appleton, Wia, assignor, by mesne assignments, to K. C. M. Company, Dayto Ohio, a corporation of Delaware No Drawing. Application June 29, 1934, Serial No. 732,994

"10 Claims.

In the operation of coating paper with materials having a mineral constituent considerable trouble has been experienced from a phenomenon known in mill parlance as dusting. This is due mainly to the fact that the mineral coating matter is insufficiently bonded together and to the paper, and results in much of the coating coming off as a dust cloud (in aggravated cases) at the rewinder, or sticking to the calender rolls until it has built up scales, which eventually detach themselves from the roll and go along with the paper; or it shows up in the print shop where it builds up on the tympan or backing sheet or sheets for the sheet of paper on which the printing is being done.

This dusting phenomenon manifests itself mainly in what are known as continuous processes; that is, processes wherein the coating is applied ,by coating rolls, dipping, or otherwise to the partly dried paper web as it comes from the web forming machine, an example of this process being shown in Letters Patent to Germanson and Kranhold, No. 1,918,095, granted July 11, 1933.

I have discovered that dusting may be greatly reduced, and in many cases, practically eliminated, by keeping the viscosity of the coating liquid substantially constant or uniform, and this is preferably done by suitably controlling the temperature of the coating fluid.

In processes such as I have described the partly dried paper web coming to the coating press is hot by reason of heat absorbed from the drying rolls, and the result is that the coating material through or in contact with which the hot web 35 passes at the coating press, itself becomes hot.

As to the reasons why hot coating causes dust ing, it is believed to be largely due to the reduced viscosity of the liquid portion of the coating at the higher temperature, which in the case of such coating mixtures as casein, clay and water, permits the liquid portion to penetrate the paper web to a greater extent, carrying with it the dissolved casein, and leaving the mineral matter (clay) on the surface without suflicient binder 45 to hold it together and in place. Furthermore,.

if the coating is held for some time at an elevated temperature it undergoes some chemical and even bacterial decomposition, which is also believed coating mixture itself as, for example, waterjacketing the mixture pan and the pipe lines through which the mixture circulates and placing cooling coils in the coating storage tanks, or both. Since mechanical embodiments of these 5 suggested cooling methods are obvious, illustrations thereof in the form of drawings are believed to be unnecessary.

The dusting nuisapce above described is harmful in at least two ways. In the first place it impairs the quality of the coated product, and in the second place, it fouls the atmosphere of the mill room in which the machine attendants are employed. I

It has been observed in laboratory studies that sheets of paper dipped or treated with hot aqueous coating solutions and pressed between rolls tend to disintegrate, loosen, swell and roughen the surface constituents of the sheet more than sheets of paper dipped or treated with a cold aqueous coating mixture. This roughening effect and loosening of the bonds of .the fibers to one another results in a finished sheet which has fibers standing up on the surface. Drying the swelled fibers also results in shrinkage and distortion of coating on the fibers. When such a sheet is calendered or brushed, coating and distended fibers rupture and break 011 on and under the surfaces of the paper. This results in what is commonly known as dust.

The application of a cold aqueous coating mixture no doubt prevents excessive accelerated swelling, decreases the tendency of breaking the bonds between fibers and results in acomparatively smooth, compact sheet. The smoother and more compact the sheet, the less danger there is of fibers and'coating breaking oil? on calendering to-form the so-called dust.

I have found by experiments that the above described method of abatin'g or lessening this dusting nuisance is most eflective in the case of coatings which contain casein as the binder, and somewhat less so in the case of starch coatings. Undoubtedly it may also be used to advantage with coating mixtures containing binders other than casein and starch.

I claim:

1. The process of, preparing a substantially non-dusting paper, as part of a continuous paper making operation, which comprises applying to a heated, partially dried web a coating composition containing an adhesive liquid fraction and an insoluble solid fraction, the coating composition at the point of application being maintained at a. temperature sufiiciently low, and 65 abstract I therefrom the at a viscosity sufilciently high, to prevent separation of the liquid fraction from the solid fraction during the coating operation.

- 2. The process as defined in claim 1 in which the said temperature" and viscosity are maintained by continuously abstracting from the coat- 4. The process as definedin claim 1 in which the said temperature and viscosity are maintained by continuousLv subjecting the coating mixture to the influence of a coolingmedium to heat imparted thereto by the heated web. l

5. The processes defined in claim 1 in which the said temperature and viscosity are maintained by continuously subjecting the heated web to the influence of a cooling medium prior to its contact with the coating mixture;

6. In a process of preparing a substantially non-dusting paper, as part of a continuous paper making operation, wherein the wet web is heated immediately before receiving a coating composition, containing an adhesive liquid fraction and an insoluble solid fraction, to partially dry the same, the improvement of preventing the tively to prevent such undesirable, rapid penetration.

7. The process as defined in claim 6 in which the said temperature and viscosity are maintained by continuously abstracting from the coating mixture the heat imparted thereto by the heated web;

- 8. The process as defined in claim 6 wherein the said temperature and viscosity are maintained by continuously abstracting from the coating mixture substantially at its point of application to the web the heat imparted to the coating mixture by the heated web.

9. The process as defined in claim 6 in which the said temperature and viscosity are maintained by continuously subjecting the coating mixture to the influence of a cooling medium to abstract therefrom the heat imparted thereto by the heated web.

10. The process as defined in claim 6 in which the said temperature and viscosity are maintained by continuously subjecting the heated web to the influence of a cooling medium prior to its contact with the coating mixture.

LOUIS C. FLECK. 

